Spatiotemporal beating and vortices of van der Waals hyperbolic polaritons

• 成果类型: Article
• 署名作者: Zhang, Tianning; Yan, Qizhi; Yang, Xiaosheng; Ma, Weiliang; Chen, Runkun; Zhang, Xin; Janzen, Eli; Edgar, James H.; Qiu, Cheng-Wei; Zhang, Xinliang; Li, Peining
• 署名单位: Huazhong University of Science & Technology; Huazhong University of Science & Technology; Kansas State University; National University of Singapore; Xidian University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8877
• DOI: 10.1073/pnas.2319465121
• 发表日期: 2024-03-19
• 关键词: negative refraction; phonon-polaritons; propagation; generation; DYNAMICS; GROWTH

摘要

In conventional thin materials, the diffraction limit of light constrains the number of waveguide modes that can exist at a given frequency. However, layered van der Waals (vdW) materials, such as hexagonal boron nitride (hBN), can surpass this limitation due to their dielectric anisotropy, exhibiting positive permittivity along one optic axis and negativity along the other. This enables the propagation of hyperbolic rays within the material bulk and an unlimited number of subdiffractional modes characterized by hyperbolic dispersion. By employing time- domain near - field interferometry to analyze ultrafast hyperbolic ray pulses in thin hBN, we showed that their zigzag reflec tion trajectories bound within the hBN layer create an illusion of backward- moving and leaping behavior of pulse fringes. These rays result from the coherent beating of hyperbolic waveguide modes but could be mistakenly interpreted as negative group velocities and backward energy flow. Moreover, the zigzag reflections produce nano scale (60 nm) and ultrafast (40 fs) spatiotemporal optical vortices along the trajectory, presenting opportunities to chiral spatiotemporal control of light-matter interac tions. Supported by experimental evidence, our simulations highlight the potential of hyperbolic ray reflections for molecular vibrational absorption nanospectroscopy. The results pave the way for miniaturized, on - chip optical spectrometers, and ultrafast optical manipulation. Significance Two- dimensional van der Waals (vdW) materials can squeeze light to subwavelength scale and support so- called hyperbolic polaritons (HPs), a peculiar light-matter interaction mode where the light is steered along conical rays. Here, we present a time- domain near - field interferometry approach to characterize the spatiotemporal beating of HPs as they undergo total internal reflections while propagating in the vdW material. These reflections produce spatiotemporal optical vortices occurring on nanometer and femtosecond scales along the trajectory. We further demonstrate the potential of utilizing highly confined HP rays to transfer spectroscopic information of molecules with a vdW material.